The many organic compounds found in living organisms-proteins and
amino acids, sugars, organic acids and bases, fats, and hormones-are
possible only because of the many different kinds of atoms and groups
of atoms that can be attached to carbon backbones. In the next chapter
we shall see what several of these compounds are like.
Before we do, however, we must look at the carbon backbones themselves.
This chapter is devoted to hydrocarbons-compounds of carbon and
hydrogen. Many of the ideas that we will develop about hydrocarbons
will carry over directly to more complicated compounds.
The special properties of carbon that make it appropriate for construction
of living organisms arise from its central position in the periodic
In the previous chapter we mentioned that life occupies the midranges
of size and temperature in the universe.
Carbon occupies the midposition in Row 2 of the periodic table,
and has exactly half as many electrons as are needed to fill. its
outer shell. It neither loses nor gains electrons in chemical reactions,
so its compounds are not ionic. This is critical for its role, since
the nondirectional electrostatic forces between ions are inadequate
for building elaborate molecules (right).